Ultrasongraphic device

ABSTRACT

An ultrasonic diagnostic apparatus is provided that can achieve an excellent image quality even in the case where a subject moves at a high speed. A memory ( 3 ) stores a first signal obtained through first-time transmission/reception. When a second signal is obtained through second-time transmission/reception, a delay amount calculator ( 6 ) calculates a delay amount for either of the first and second signals based on first and second timings outputted respectively from first and second zero crossing detectors ( 4, 5 ), at which the first and second signals cross zero, respectively. Delayers ( 7, 8 ) delay the first or second signal by the calculated delay amount so that phases of the signals are matched with each other. An adder ( 9 ) adds together the two signals whose phases have been matched.

TECHNICAL FIELD

The present invention relates to an ultrasonic diagnostic apparatus thatmakes an observation and a diagnosis of the state of a subject such as aliving body or the like by performing synthetic aperture scanning inwhich a plurality of times of transmission/reception of ultrasonic beamsis performed by arrayed transducer-elements.

BACKGROUND ART

In recent years, an ultrasonic diagnostic apparatus that performssynthetic aperture scanning has been known. Such an ultrasonicdiagnostic apparatus has been introduced in P. D. Corl, et al. “Adigital synthetic imaging system for NDE”, Proc IEEE Ultrasonics Symp.,Sept. 1978. The following description is directed to the principle ofthe operation of the ultrasonic diagnostic apparatus with reference toFIG. 3. FIG. 3 is a block diagram schematically showing an example ofthe configuration of an ultrasonic diagnostic apparatus using syntheticaperture scanning in Conventional Example 1.

In FIG. 3, an ultrasonic probe 1 is composed of a plurality oftransducer-elements T1 to T8. The transducer-element Tn (n=1 to 8)generates ultrasonic pulses, and the ultrasonic pulses reflected in asubject are received by the transducer-element Tn as an echo ultrasonicwave. A received signal received by the transducer-eleinent Tn passesthrough a multiplexer (MUX 100 and is amplified by an amplifier 102. Thereceived signal then is converted into digital data by an A/D 103 andwritten into a memory 104. Upon completion of the writing of thereceived signal from the transducer-element Tn into the memory 104, theMUX 100 subsequently selects the transducer-element Tn′ that isdifferent from the transducer-element Tn, and in the same manner as inthe case of the transducer-element Tn, a received signal is written intothe memory 104. In the above-described manner, received signals obtainedby the transducer-elements T1 to T8 are written into the memory 104.Next, in an adder 105, output signals from the memory 104, namely, thereceived signals obtained by the transducer-elements T1 to T8 that havebeen stored in the memory 104, are added together after being providedwith respective predetermined time differences.

Transmission/reception sequences (the above-described series oftransmission/reception operations are referred to as atransmission/reception sequence) by the transducer-elements T1 to T8 areperformed one by one in the above-described manner, and signals areintegrated. Thus, the same effect as in the case of simultaneousreception by the eight transducer-elements can be obtained.

Assuming that the subject stays at rest during the periods of receptionby the transducer-elements T1 to T8, in the subject, receivingdirectivity for beam convergence, beam deflection or the like can beimparted to the ultrasonic probe 1.

The received signals added by the adder 105 as described above aresubjected to signal processing such as detection or the like by a signalprocessor 106 and displayed on a display part 107.

However, the above-described conventional ultrasonic diagnosticapparatus having a synthetic aperture has presented a problem that asynthetic aperture cannot be operated accurately in the case where asubject has moved during the periods of reception by thetransducer-elements T1 to T8.

By referring to FIG. 4, the description is directed next to a method forimproving a synthetic aperture in the case where a subject moves. FIG. 4is a block diagram schematically showing an example of the configurationof the ultrasonic diagnostic apparatus using the synthetic aperturescanning as Conventional Example 2.

In FIG. 4, a probe 1 is composed of transducer-elements T1 to T8. Theprobe 1 is driven with high-voltage pulses generated by a transmittingcircuit 108 and irradiates ultrasonic waves into a body that is notshown. Ultrasonic signals reflected in the body are received by thetransducer-elements T1 to T8 and converted into electric signals. Thistransmission/reception sequence is performed twice. In first-timetransmission/reception, switches 109 to 112 are connected with a-sidecontacts and select received signals from the transducer-elements T1 toT4, respectively. The signals that have passed though the SW 109 to 112are converted into digital signals by A/D converters 113 to 116,respectively, and a beam is synthesized by a beam synthesizer 117. Asignal obtained in the first-time transmission/reception is stored in amemory 119 in an aperture adding part 118.

Subsequently, second-time transmission/reception is performed. In thiscase, the SW 109 to 112 are switched so as to be connected with b-sidecontacts, and the transducer-elements T5 to T8 are selected. In the samemanner as in the case of the first-time transmission/reception, receivedsignals from the transducer-elements T5 to T8 are converted into digitalsignals by the A/D converters 113 to 116, respectively, and beamsynthesizing is performed by the beam synthesizer 117. By an adder 120,a received signal obtained through the second-timetransmission/reception is added to the signal obtained in the first-timetransmission/reception that has been stored in the memory 119. Afterthat, the signals are detected by a wave detector 121, scanned andconverted by a digital scan converter ODSC) 122, and displayed on adisplay part 107.

As described above, in the method employed in the case of ConventionalExample 2, the transmission/reception sequences for a synthetic apertureconsist of two times of transmission/reception, and therefore, comparedwith the case of the synthetic aperture of Conventional Example 1, lessinfluence is exerted by the movement of a subject.

However, the method employed in the case of Conventional Example 2 alsopresents the following problem. That is, according to the speed of themovement of a subject, a phase difference is caused between a signalobtained through first-time transmission/reception and a signal obtainedthrough second-time transmission/reception, and the signals cancel eachother when added by the adder 120. In the case where the cancellation isof such a high degree as to affect an image, the image quality might bedeteriorated by the influence of the movement.

DISCLOSURE OF INVENTION

With the foregoing in mind, it is an object of the present invention toprovide an ultrasonic diagnostic apparatus that can achieve an excellentimage quality even in the case where a subject moves at a high speed.That is, the present invention is to obtain an ultrasonic diagnosticapparatus that eliminates a phase difference between signals caused dueto the movement of a subject during a plurality of times oftransmission/reception by a synthetic aperture, thereby achieving anexcellent image quality.

In order to achieve the above-mentioned object, a first ultrasonicdiagnostic apparatus according to the present invention is an ultrasonicdiagnostic apparatus using synthetic aperture scanning in which one beamis synthesized through a plurality of times of transmission/receptionand includes: a transmitting circuit that transmits driving pulses aplurality of times; a plurality of arrayed transducer-elements, each ofwhich emits an ultrasonic beam from an aperture according to the drivingpulses, receives the ultrasonic beam reflected in a subject by means ofthe aperture, and outputs a received signal; switches that selectivelyoutput a plurality of signals from among the received signals outputtedfrom the arrayed transducer-elements; a beam synthesizer that performsbeam formation based on the signals selected by the switches; a memorythat temporarily stores each of signals outputted from the beamsynthesizer as a result of the plurality of times oftransmission/reception; and an adder that adds together the signals inthe memory that correspond respectively to the plurality of times oftransmission/reception. The ultrasonic diagnostic apparatus furtherincludes: a unit for detecting a phase difference between the signalsobtained through the plurality of times of transmission/reception; and adelay unit that outputs to the adder the signals obtained through theplurality of times of transmission/reception while matching phases ofthe signals with each other. In this case, as the plurality of times oftransmission/reception, for example, two times of transmission/receptionare performed.

According to this configuration, a phase difference between a receivedsignal obtained through first-time transmission/reception and a receivedsignal obtained through second-time transmission/reception iseliminated, and thus the deterioration of an image quality can beprevented.

Preferably, in the first ultrasonic diagnostic apparatus, the unit fordetecting a phase difference includes: a plurality of zero crossingdetectors, each of which detects a timing at which an amplitude of eachof the signals that correspond respectively to the plurality of times oftransmission/reception shifts from a positive polarity to a negativepolarity or vice versa to cross zero; and a unit for calculating a delayamount with respect to the signals obtained through the plurality oftimes of transmission/reception based on the timing detected by each ofthe plurality of zero crossing detectors.

This enables easy correction of a phase difference between signalsobtained through a plurality of times of transmission/reception.

In order to achieve the above-mentioned object, a second ultrasonicdiagnostic apparatus according to the present invention is an ultrasonicdiagnostic apparatus using synthetic aperture scanning in which one beamis synthesized through a plurality of times of transmission/receptionand includes: a transmitting circuit that transmits driving pulses aplurality of times; a plurality of arrayed transducer-elements, each ofwhich emits an ultrasonic beam from an aperture according to the drivingpulses, receives the ultrasonic beam reflected in a subject by means ofthe aperture, and outputs a received signal; switches that selectivelyoutput a plurality of signals from among the received signals outputtedfrom the arrayed transducer-elements; a beam synthesizer that performsbeam formation based on the signals selected by the switches; a memorythat temporarily stores each of signals outputted from the beamsynthesizer as a result of the plurality of times oftransmission/reception; and an adder that adds together the signals inthe memory that correspond respectively to the plurality of times oftransmission/reception. The ultrasonic diagnostic apparatus furtherincludes a plurality of wave detectors that perform amplitude detectionof the signals obtained through the plurality of times oftransmission/reception and output the signals to the adder. In thiscase, as the plurality of times of transmission/reception, for example,two times of transmission/reception are performed.

According to this configuration, canceling-out of signals caused due toa phase difference is prevented, and thus the deterioration of an imagequality can be prevented.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram schematically showing an example of theconfiguration of an ultrasonic diagnostic apparatus using syntheticaperture scanning according to Embodiment 1 of the present invention.

FIG. 2 is a block diagram schematically showing an example of theconfiguration of an ultrasonic diagnostic apparatus using syntheticaperture scanning according to Embodiment 2 of the present invention.

FIG. 3 is a block diagram schematically showing an example of theconfiguration of an ultrasonic diagnostic apparatus using syntheticaperture scanning as Conventional Example 1.

FIG. 4 is a block diagram schematically showing an example of theconfiguration of the ultrasonic diagnostic apparatus using the syntheticaperture scanning as Conventional Example 2.

DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described by way of preferredembodiments with reference to the appended drawings.

Embodiment 1

FIG. 1 is a block diagram schematically showing an example of theconfiguration of an ultrasonic diagnostic apparatus using syntheticaperture scanning according to Embodiment 1 of the present invention. InFIG. 1, the same reference numerals indicate the respective parts havingsimilar configurations and functions to those in FIG. 4 referred to fordescribing Conventional Example 2 so as to avoid duplicate descriptionsthereof.

In FIG. 1, in the same manner as in the case of Conventional Example 2,using a probe 1, signals for a synthetic aperture are received throughtwo times of transmission/reception, and beam synthesization isperformed. This embodiment is different from Conventional Example 2 inthe configuration of an aperture adding part.

An aperture adding part 2 is composed of a memory 3 that stores a signal(first signal) obtained through first-time transmission/reception; afirst zero crossing detector 4 that detects a first timing at which anamplitude of the first signal obtained through the first-timetransmission/reception shifts from a positive polarity to a negativepolarity or vice versa to cross zero; a second zero crossing detector 5that detects a second timing at which an amplitude of a second signalobtained through second-time transmission/reception shifts from apositive polarity to a negative polarity or vice versa to cross zero; adelay amount calculator 6 that calculates, based on the first and secondtimings outputted from the two zero crossing detectors 4 and 5, a delayamount determining whether and how much the first signal or the secondsignal should be delayed in order that phases of the first signal andthe second signal are matched with each other; delayers 7 and 8 fordelaying the first signal or the second signal by the delay amountcalculated by the delay amount calculator 6; and an adder 9 that addstogether the two signals whose phases have been matched by delaying.

The above-described configuration operates as follows. Initially,first-time transmission/reception is performed, and a received signal(first signal) is accumulated in the memory 3. Subsequently, second-timetransmission/reception is performed to obtain a received signal (secondsignal), and based on this received signal, the first timing at whichthe received signal shifts from a positive polarity to a negativepolarity or vice versa is detected by the zero crossing detector 5. Atthe same time, the received signal obtained through the first-timetransmission/reception is read out from the memory 3, and the secondtiming at which the received signal shifts from a positive polarity to anegative polarity or vice versa is detected by the zero crossingdetector 4. Based on information of the first and second timingsdetected by the two zero crossing detectors 4 and 5, it is judged by thedelay amount calculator 7 whether and how much the first signal or thesecond signal is advanced (delayed). Delay amounts for the delayers 7and 8 are adjusted so that phases of the received signals are adjustedto be the same, and the received signals are added together by the adder9.

As described above, according to this embodiment, even in the case wherea subject moves at a high speed, a phase difference between a receivedsignal obtained through first-time transmission/reception and a receivedsignal obtained through second-time transmission/reception iseliminated, and thus the deterioration of an image quality can beprevented.

In this embodiment, the memory 3 is located upstream of the zerocrossing detector 4. However, this order of arrangement may be reversed.In that case, when a received signal is captured in the memory 3 as aresult of first-time transmission/reception, the first timing at whichthe received signal shifts from a positive polarity to a negativepolarity or vice versa could be detected and stored in the delay amountcalculator 7.

Furthermore, this embodiment uses the timing detection by the zerocrossing detectors 4 and 5 in which a timing at which an amplitude of asignal shifts from a positive polarity to a negative polarity or viceversa to cross zero is detected because it enables easy phase detection.However, other methods such as, for example, a method using a frequencyanalysis also may be used.

Embodiment 2

FIG. 2 is a block diagram schematically showing an example of theconfiguration of an ultrasonic diagnostic apparatus using syntheticaperture scanning according Embodiment 2 of the present invention. InFIG. 2, the same reference numerals indicate the respective parts havingsimilar configurations and functions to those in FIGS. 4 and 1 referredto for describing Conventional Example 2 and Embodiment 1, respectively,so as to avoid duplicate descriptions thereof.

In FIG. 2, in the same manner as in the cases of Conventional Example 2and Embodiment 1, using a probe 1, signals for a synthetic aperture arereceived through two times of transmission/reception, and beamsynthesization is performed. This embodiment is different fromEmbodiment 1 in the configuration of an aperture adding part and doesnot require a wave detector 121.

In FIG. 2, an aperture adding part 10 is composed of a memory 3 thatstores a received signal (first signal) obtained through first-timetransmission/reception; a wave detector 11 that detects the receivedsignal first signal) obtained through the first-timetransmission/reception; a wave detector 12 that detects a receivedsignal (second signal) obtained through second-timetransmission/reception; and an adder 13 that adds together the first andsecond signals that have been detected.

As described above, according to this embodiment, each of phaseinformations on a received signal obtained through first-timetransmission/reception and a received signal obtained throughsecond-time transmission/reception is eliminated through amplitudedetection by the wave detectors 11 and 12, so that only amplitudeinformation remains. This prevents cancellation between the signals dueto a phase difference, and thus even in the case where a subject movesat a high speed, the deterioration of an image quality can be prevented.

Furthermore, according to this embodiment, compared with Embodiment 1,the number of constituent components of the apparatus can be reduced.

The same effect can be obtained also in the case where the memory 3 islocated downstream of the wave detector 11.

As described in the foregoing discussion, according to the presentinvention, when performing synthetic aperture scanning, phases ofreceived signals, each obtained every time transmission/reception isperformed, are detected and matched with each other, thereby preventingcanceling-out of the signals due to a phase difference caused when asubject moves, and thus an image of an excellent quality can beobtained.

1. An ultrasonic diagnostic apparatus using synthetic aperture scanningin which one beam is synthesized through a plurality of times oftransmission/reception, comprising: a transmitting circuit thattransmits driving pulses a plurality of times; a plurality of arrayedtransducer-elements, each of which emits an ultrasonic beam from anaperture according to the driving pulses, receives the ultrasonic beamreflected in a subject by means of the aperture, and outputs a receivedsignal; switches that selectively output a plurality of signals fromamong the received signals outputted from the arrayedtransducer-elements; a beam synthesizer that performs beam formationbased on the signals selected by the switches; a memory that temporarilystores each of signals outputted from the beam synthesizer as a resultof the plurality of times of transmission/reception; and an adder thatadds together the signals in the memory that correspond respectively tothe plurality of times of transmission/reception, wherein the apparatusfurther comprises: a unit for detecting a phase difference between thesignals obtained through the plurality of times oftransmission/reception; and a delay unit that outputs to the adder thesignals obtained through the plurality of times oftransmission/reception while matching phases of the signals with eachother.
 2. The ultrasonic diagnostic apparatus according to claim 1,wherein the plurality of times of transmission/reception is two times.3. The ultrasonic diagnostic apparatus according to claim 1, wherein theunit for detecting a phase difference comprises: a plurality of zerocrossing detectors, each of which detects a timing at which an amplitudeof each of the signals that correspond respectively to the plurality oftimes of transmission/reception shifts from a positive polarity to anegative polarity or vice versa to cross zero; and a unit forcalculating a delay amount with respect to the signals obtained throughthe plurality of times of transmission/reception based on the timingdetected by each of the plurality of zero crossing detectors.
 4. Anultrasonic diagnostic apparatus using synthetic aperture scanning inwhich one beam is synthesized through a plurality of times oftransmission/reception, comprising: a transmitting circuit thattransmits driving pulses a plurality of times; a plurality of arrayedtransducer-elements, each of which emits an ultrasonic beam from anaperture according to the driving pulses, receives the ultrasonic beamreflected in a subject by means of the aperture, and outputs a receivedsignal; switches that selectively output a plurality of signals fromamong the received signals outputted from the arrayedtransducer-elements; a beam synthesizer that performs beam formationbased on the signals selected by the switches; a memory that temporarilystores each of signals outputted from the beam synthesizer as a resultof the plurality of times of transmission/reception; and an adder thatadds together the signals in the memory that correspond respectively tothe plurality of times of transmission/reception, wherein the apparatusfurther comprises a plurality of wave detectors that perform amplitudedetection of the signals obtained through the plurality of times oftransmission/reception and output the signals to the adder.
 5. Theultrasonic diagnostic apparatus according to claim 4, wherein theplurality of times of transmission/reception is two times.